Re: For review: seccomp_user_notif(2) manual page

From: Tycho Andersen <tycho@tycho.pizza>
To: Sargun Dhillon <sargun@sargun.me>
Cc: "Michael Kerrisk (man-pages)" <mtk.manpages@gmail.com>,
	Kees Cook <keescook@chromium.org>,
	Christian Brauner <christian@brauner.io>,
	linux-man <linux-man@vger.kernel.org>,
	lkml <linux-kernel@vger.kernel.org>,
	Aleksa Sarai <cyphar@cyphar.com>, Jann Horn <jannh@google.com>,
	Alexei Starovoitov <ast@kernel.org>,
	Will Drewry <wad@chromium.org>,
	bpf@vger.kernel.org, Song Liu <songliubraving@fb.com>,
	Daniel Borkmann <daniel@iogearbox.net>,
	Andy Lutomirski <luto@amacapital.net>,
	Linux Containers <containers@lists.linux-foundation.org>,
	Giuseppe Scrivano <gscrivan@redhat.com>,
	Robert Sesek <rsesek@google.com>
Subject: Re: For review: seccomp_user_notif(2) manual page
Date: Thu, 1 Oct 2020 17:19:15 -0600	[thread overview]
Message-ID: <20201001231915.GA16219@cisco> (raw)
In-Reply-To: <CAMp4zn9XA-z_6UKvWkFh_U2wPRjZF3=QvrXX7EikO5AEovCWBA@mail.gmail.com>

On Thu, Oct 01, 2020 at 02:06:10PM -0700, Sargun Dhillon wrote:
> On Wed, Sep 30, 2020 at 4:07 AM Michael Kerrisk (man-pages)
> <mtk.manpages@gmail.com> wrote:
> >
> > Hi Tycho, Sargun (and all),
> >
> > I knew it would be a big ask, but below is kind of the manual page
> > I was hoping you might write [1] for the seccomp user-space notification
> > mechanism. Since you didn't (and because 5.9 adds various new pieces
> > such as SECCOMP_ADDFD_FLAG_SETFD and SECCOMP_IOCTL_NOTIF_ADDFD
> > that also will need documenting [2]), I did :-). But of course I may
> > have made mistakes...
> >
> > I've shown the rendered version of the page below, and would love
> > to receive review comments from you and others, and acks, etc.
> >
> > There are a few FIXMEs sprinkled into the page, including one
> > that relates to what appears to me to be a misdesign (possibly
> > fixable) in the operation of the SECCOMP_IOCTL_NOTIF_RECV
> > operation. I would be especially interested in feedback on that
> > FIXME, and also of course the other FIXMEs.
> >
> > The page includes an extensive (albeit slightly contrived)
> > example program, and I would be happy also to receive comments
> > on that program.
> >
> > The page source currently sits in a branch (along with the text
> > that you sent me for the seccomp(2) page) at
> > https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/log/?h=seccomp_user_notif
> >
> > Thanks,
> >
> > Michael
> >
> > [1] https://lore.kernel.org/linux-man/2cea5fec-e73e-5749-18af-15c35a4bd23c@gmail.com/#t
> > [2] Sargun, can you prepare something on SECCOMP_ADDFD_FLAG_SETFD
> >     and SECCOMP_IOCTL_NOTIF_ADDFD to be added to this page?
> >
> > ====
> >
> > --
> > Michael Kerrisk
> > Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
> > Linux/UNIX System Programming Training: http://man7.org/training/
> 
> Should we consider the SECCOMP_GET_NOTIF_SIZES dance to be "deprecated" at
> this point, given that the extensible ioctl mechanism works? If we add
> new fields to the
> seccomp datastructures, we would move them from fixed-size ioctls, to
> variable sized
> ioctls that encode the datastructure size / length?
> 
> -- This is mostly a question for Kees and Tycho.

It will tell you how big struct seccomp_data in the currently running
kernel is, so it still seems useful/necessary to me, unless there's
another way to figure that out.

But I agree, I don't think the intent is to add anything else to
struct seccomp_notif. (I don't know that it ever was.)

Tycho